The present invention pertains to an electrolytic copper plating method and a pure copper anode used in such electrolytic copper plating method capable of suppressing the generation of particles such as sludge produced on the anode side within the plating bath upon performing electrolytic copper plating, and in particular capable of preventing the adhesion of particles to a semiconductor wafer, as well as to a semiconductor wafer having low particle adhesion plated with the foregoing method and anode.
Generally, although an electrolytic copper plate has been employed for forming copper wiring in a PWB (print wiring board) or the like, in recent years, it is being used for forming copper wiring of semiconductors. An electrolytic copper plate has a long history, and it has reached its present form upon accumulating numerous technical advancements. Nevertheless, when employing this electrolytic copper plate for forming copper wiring of semiconductors, a new problem arose which was not found in a PWB.
Ordinarily, when performing electrolytic copper plating, phosphorous copper is used as the anode. This is because when an insoluble anode formed from the likes of platinum, titanium, or iridium oxide is used, the additive within the plating liquid would decompose upon being affected by anodic oxidization, and inferior plating will occur thereby. Moreover, when employing electrolytic copper or oxygen-free copper of a soluble anode, a large amount of particles such as sludge is generated from metallic copper or copper oxide caused by the dismutation reaction of monovalent copper during dissolution, and the plating object will become contaminated as a result thereof.
On the other hand, when employing a phosphorous copper anode, a black film composed of phosphorous copper or copper chloride is formed on the anode surface due to electrolysis, and it is thereby possible to suppress the generation of metallic copper or copper oxide caused by the dismutation reaction of monovalent copper, and to control the generation of particles.
Nevertheless, even upon employing phosphorous copper as the anode as described above, it is not possible to completely control the generation of particles since metallic copper or copper oxide is produced where the black film drops off or at portions where the black film is thin.
In light of the above, a filter cloth referred to as an anode bag is ordinarily used to wrap the anode so as to prevent particles from reaching the plating liquid.
Nevertheless, when this kind of method is employed, particularly in the plating of a semiconductor wafer, there is a problem in that minute particles, which were not a problem in forming the wiring of a PWB and the like, reach the semiconductor wafer, such particles adhere to the semiconductor, and thereby cause inferior plating.
As a result, when employing phosphorous copper as the anode, it became possible to significantly suppress the generation of particles by adjusting the phosphorous content, which is a component of phosphorous copper, electroplating conditions such as the current density, crystal grain diameter and so on.
Nevertheless, when the phosphorous copper anode dissolves, since phosphorous elutes simultaneously with copper in the solution, a new problem arose in that the plating solution became contaminated by the phosphorous. Although this phosphorous contamination occurred in the plating process of conventional PWB as well, as with the foregoing cases, it was not much of a problem. However, since the copper wiring of semiconductors and the like in particular disfavor eutectoid and inclusion of impurities, phosphorous accumulation in the solution was becoming a major problem.